This invention relates to new s-triazine prepolymers and a process for their preparation.
It is known to polymerise difunctional or polyfunctional aromatic cyanic acid esters to give high molecular polytriazines (German Published Specification 1,190,184). The polymerisation takes place strongly exothermically and with relatively great shrinkage, via a so-called "B-stage" (Kunststoffe, volume 58, page 829 (1968)); this results in various disadvantages, particularly as regards conversion to, for example, glass fibre-reinforced mouldings and, for example, the dimensional accuracy of the mouldings produced. It has already been proposed to avoid the disadvantages of the direct polymerisation by preparing prepolymers by interrupting the polymerisation, by cooling, when about 30 to 65% of the cyanic acid ester groups have reacted (British Pat. No. 1,305,762).